Avoid alliteration. Always.

Prepositions are not words to end sentences with.

Avoid cliches like the plague. (They're old hat.)

Employ the vernacular.

Eschew ampersands & abbreviations, etc.

Parenthetical remarks (however relevant) are unnecessary.

It is wrong to ever split an infinitive.

Contractions aren't necessary.

Foreign words and phrases are not apropos.

One should never generalize.

Eliminate quotations. As Ralph Waldo Emerson once said: "I hate quotations. Tell me what you know."

Comparisons are as bad as cliches.

Don't be redundant; don't more use words than necessary; it's highly superfluous.

Be more or less specific.

Understatement is always best.

Exaggeration is a billion times worse than understatement.

One-word sentences? Eliminate.

Analogies in writing are like feathers on a snake.

The passive voice is to be avoided.

Go around the barn at high noon to avoid colloquialisms.

Even if a mixed metaphor sings, it should be derailed.

Who needs rhetorical questions?

While a transcendent vocabulary is laudable, one must nevertheless keep incessant surveillance against such loquacious, effusive, voluble verbosity that the calculated objective of communication becomes ensconced in obscurity.

In a sentence, the nouns has to match the verbs.

Don't use no double negatives.

In writing, few things are, so to speak, more infuriating, than, say, commas, at least when there are too many of them, or when they should be, say, semicolons.

Proofread your work, so you don't leave some out or forget to finish

Run-on sentences are really bad because the reader saturates and what you really should be doing is using commas and semicolons and even periods to break the sentence up into more digestible chunks.

To have been using excessively complex verb constructions, is to have been bopping the literary baloney.

A friend I spoken with recently told me he been forgetting his helper verbs.